1. Field of the Invention
This application is directed to the art of composite brake shoes.
2. Description of Related Art
Railcars are supported and guided by steel wheels. The treads at the outer circumference of the wheels ride over steel rails. Railcar brakes comprise brake shoes that are brought into frictional engagement with the wheel treads. The brake shoes are supported by brake heads which, in turn, are movably supported by the brake rigging comprised of a system of levers and a pneumatic cylinder. Brake shoes are comprised of various materials that are selected for their frictional characteristics and for the effect on the wear life of the wheel treads. Many brake shoes are composites of materials having different characteristics. In typical composite brakes shoes, materials of differing frictional characteristics bear upon the wheel tread during braking. This may be achieved by placing inserts of a different material into the friction face of the shoe comprised of the principal brake shoe material.
Standard railway brake shoes in North America are produced with metal backing plates for support of the friction material and for attachment and retention of the brake shoes to the brake heads. Elsewhere in the world, brake shoes are produced without metal backing plates and normally include a skeletal wire frame. One type of railway brake shoe also includes a metallic insert solidly affixed by welding to the metal backing plate before the brake pad is formed, for example, by molding, onto the backing plate. See U.S. Pat. No. 6,241,058 entitled “Brake Shoe with Insert Bonded to Backing Plate.” Recently, metallic inserts have been introduced into brake shoes without the metal backings as taught in PCT/US2007/069854 entitled “Railway Brake Shoe.”
The brake shoe friction material often comprises a blend of abrasive materials, organic and inorganic filler materials, and resins. The metallic insert may be selected to provide beneficial treatment of the rolling surface of the wheel.
Fiber reinforced resilient backing layers between the friction material and metal backing plates have been suggested to attenuate sound. See U.S. Pat. No. 4,371,631 entitled “Backing Plate Composition for Brake Shoes.”